Static electricity variously occurs and is discharged in accordance with the generation sources thereof, such as frictional charging, contact charging and separation charging, and the generation place thereof. Such occurrence, increase and decrease of charges entail various problems in the use and processing of many industrial products and material. Static electrical charges cause materials to adhere to or repel each other, and raise the problems during product manufacturing and problems of pollution. Static electricity entails serious problems such as the destruction of devices and the malfunction of measuring instruments.
In the manufacture of a flexible display using a flexible substrate, such as a plastic substrate, according to the trend toward the use of light parts and thin parts in the field of industrial manufacturing, problems related to static electricity remain.
Recently, the use of an adhesive and a substrate for transporting a flexible substrate using a process of manufacturing a Liquid Crystal Display (LCD) panel or an Organic Light Emitting Display (OLED) panel, which is one of the conventional methods of manufacturing a flexible display, has been proposed. The method comprises attaching a flexible substrate to a transportation support formed of a relatively thick glass plate or plastic plate directly using the conventional process and apparatus for manufacturing a liquid crystal display device and then detaching the flexible substrate.
A double-sided adhesive tape, one side of which has low adhesiveness and the other side of which has a relatively high adhesiveness, a temperature sensitive adhesive, the adhesiveness of which varies with temperature, and a photosensitive adhesive, the adhesiveness of which is controlled by using light, have been proposed as a general adhesive for use in the above method. When such adhesives are used, there are advantages in that panel manufacturing lines that use the commonly used glass substrate can be used without variation, so that the investment cost of equipment for manufacturing panels comprising the flexible substrate is minimized, with the result that the panel can be manufactured at low cost. Technologies related thereto are as follows.
Japanese Unexamined Patent Publication Nos. Heisei08-53156, 2000-252342 and 2002-258252 disclose temperature sensitive adhesives which have high adhesiveness at the time of the transport and processing of electronic parts and facilitate the peeling of the electronic parts due to the increase in adhesiveness with temperature after the transport and processing thereof.
Japanese Unexamined Patent Publication No. Heisei08-53156 discloses an adhesive using a (meth)acrylic acid polymer having side-chain crystallinity, in which the carbon number of an ester thereof is 8 or more. In this cold-peelable adhesive, the ratio of the adhesiveness at a temperature lower than the melting point to the adhesiveness at a temperature higher than the melting point is from 1/1 to 1/4. Therefore, a substrate cannot be detached in a high-temperature process, but can be easily detached at a temperature lower than the (melting point −10)° C.
Japanese Unexamined Patent Publication No. 2000-252342 discloses a double-sided adhesive tape one side of which is coated with a warm-peelable adhesive and the other side of which is coated with an adhesive for bonding a support plate, like a conventional adhesive. The warm-peelable adhesive has an advantage in that, when the warm-peelable adhesive is heated to a temperature of 100° C. for 1 minute, the adhesion area is decreased due to foaming, so that the adhesiveness is decreased, thereby the warm-peelable adhesive is easily peeled off from the flexible substrate.
Japanese Unexamined Patent Publication No. 2002-258252 discloses a method of using a temperature sensitive adhesive, the adhesiveness of which varies according to a reversible change between a crystal state and an amorphous state.
However, since the adhesives described above are adhesives that contain an acrylic resin as a principal component, the properties of the adhesive are easily changed, the chemical resistance thereof is decreased, and bubbles are generated at a temperature of 150° C. or more in a Thin Film Transistor (TFT) process and/or a color filter process, which are substrate manufacturing processes for manufacturing an LCD panel or an OLED panel, therefore there is a problem in that a lithography process cannot be performed due to the low dimensional stability of the flexible, especially a plastic substrate.
Further, Japanese Unexamined Patent Publication No. 2003-27017 discloses a double-sided adhesive tape formed of a three-layered structure including a UV adhesive layer, a substrate and an adhesive layer, laminated in that order.
This double-sided tape can be easily detached by ultraviolet irradiation after processes for the liquid crystal display panel are finished, because a UV adhesive is applied to the surface of the flexible substrate on which the double sided tape is attached. However, oligomers or monomers contained in the UV adhesive are volatilized at high temperatures, thereby generating bubbles in the flexible substrate and causing the flexible substrate to peel off. A UV initiator contained in the UV adhesive can cause polymerization and curing by heating. Accordingly, even though a polymerization inhibitor is added, organic monomolecules such as oligomers or monomers are volatilized at high temperature, thereby generating bubbles in the flexible substrate.
Meanwhile, Japanese Unexamined Patent Publication No. Heisei08-086993 discloses a jig for transporting a flexible substrate, which is provided with a support that includes a pressure sensitive adhesive layer. That is, disclosed is a method of decreasing stress by forming an adhesive layer or an intermediate layer between the support of the jig and the pressure sensitive adhesive layer to prevent bubbles or peeling between the substrate and the pressure sensitive adhesive layer resulting from the stress generated by the difference in the thermal expansion coefficient. This method has an advantage in that the adhesiveness between the support and the pressure sensitive adhesive layer is increased due to the adhesive layer, thereby enabling easy removal of the flexible substrate in the final process. Although it is described in this patent document that silicon rubber, having better heat-resistance than acrylic resin, is used as the pressure sensitive adhesive, and that a jig provided with a pressure sensitive adhesive can be used several times, there have been problems in that, after the pressure sensitive adhesive has been used several times, the adhesive strength of the adhesive is decreased because extraneous materials adhere to the surface of the pressure sensitive adhesive, and the removal of the adhesive for reuse of the support cannot be easily conducted.
Even in the process of using the above tape or adhesive for transporting a substrate, static electricity can be frequently generated, and, particularly, easily generated at the time of attaching an adhesive or peeling off a release paper. Filth and dust are attached to the adhesive due to the formation or increase of static charges, and the attached pollutants deteriorate the flatness of the substrate and cause the generation of bubbles, thereby producing bad displays. Further, the generated static electricity causes the loss of adhesive or bad dimensional stability of the flexible substrate due to the phenomenon of adhesives adhering to each other, a phenomenon of an adhesive not being attached to a desired position on a support when the adhesive is attached to the support, and a phenomenon in which bubbles are generated between the adhesive and the support. Meanwhile, static electricity can be generated on the surface of the substrate even in the process of detaching the adhesive from the flexible substrate, after the processes for manufacturing the display are finished. This generated static electricity causes filth and dust to be adsorbed on the substrate or damages devices. Accordingly, it is necessary to provide antistatic properties for the adhesive for transporting the flexible substrate having heat resistance, chemical resistance and dimensional stability.
The static electricity can be prevented by removing and moving charges. The method of preventing the static electricity includes a method of using a ground, a method of increasing atmospheric humidity, a method of using a magnetic discharge type or a radiation type dust remover, a method of ionizing air, and a method of using an antistatic agent. Considering that the antistatic properties are provided for an adhesive and that the adhesive is used for electronic materials, it is preferred that the method of using the antistatic agent be used as the method of preventing static electricity because the method of using a ground, the method of increasing atmospheric humidity, the method of using a magnetic discharge type or a radiation type dust remover and the method of ionizing air pollute different electronic materials secondarily, and do not fundamentally prevent static electricity.
The antistatic agents are classified into an outer antistatic agent, which is superficially applied, and an inner antistatic agent, which is mixed in an insulating material. Generally, since the static electricity is generated, increased and decreased on the surfaces of material and moves through the surfaces of material, the inner antistatic agent, which concentrates the surface of the material and easily moves into/out of the material, is efficiently used.
Generally, a method of mixing a conductive powder with a silicon adhesive is used to provide antistatic properties for the silicon adhesive. However, when the conductive powder, which has a high specific gravity, is not mixed in a large amount, conductivity is insufficient. In contrast, when the conductive powder is mixed in a large amount, viscosity is high and workability is decreased.
Japanese Unexamined Patent Publication No. Heisei01-287169 discloses a method of preparing a silicon rubber composition having stabilized workability by diluting the composition with an organic solvent and suppressing the increase of viscosity of the composition itself. However, there are problems in that the antistatic properties and conductivity are not stabilized due to the bad precipitation and dispersion of the conductive powder, and that the low heat resistance due to the oxidation of metal powder at high temperature is not overcome.
Japanese Unexamined Patent Publication No. 2001-146578 discloses an electrically conductive silicone adhesive composition in which high heat resistance is compatible with conductivity as a conductive powder including metal powder and metal coated powder. However, there have been problems in that expensive metal powder such as copper or platinum is used, and the metal powder precipitates due to the high specific gravity thereof with the passage of time. When the metal coated powder is used, low specific gravity and conductivity are imparted to the composition, but there is a problem in that metal is peeled off due to insufficient adhesiveness between the metal powder and the metal coated powder at high temperature.
In contrast, Japanese Unexamined Patent Publication No. 2004-91750 discloses an electroconductive silicone adhesive composition, in which the silicon composition having a reducing property is applied on a substrate containing an inorganic or organic resin powder, and conductive powder coated with metal by plating is formed on the substrate, thereby lowering the specific gravity and increasing the oxidation resistance and preventing separation of the conductive powder. However, when the added powder is formed of metal and is dispersed in an adhesive due to a sizing agent, there is a problem in that the adhesive is not optically transparent, and thus the adhesive impedes the use of alignment marks of an electrode pattern at the time of manufacturing a display.
Meanwhile, carbon black, a semiconductor, or the like is used as an antistatic agent. However, since this antistatic agent does not maintain transparency at the time of the addition of the antistatic agent to an adhesive, optical properties are decreased.